1. Field of the Invention
This invention relates to communications and, more particularly, to a wireless communications access system and method.
2. Description of Related Art
Wireless communications systems include conventional cellular communication systems which comprise a number of cell sites or base stations, geographically distributed to support transmission and receipt of communication signals to and from wireless units which may actually be stationary or fixed. Each cell site handles voice communications over a particular region called a cell, and the overall coverage area for the cellular communication system is defined by the union of cells for all of the cell sites, where the coverage areas for nearby cell sites overlap to some degree to ensure (if possible) contiguous communications coverage within the outer boundaries of the system's coverage area.
When active, a wireless unit receives signals from at least one base station or cell site over a forward link or downlink and transmits signals to (at least) one cell site or base station over a reverse link or uplink. There are many different schemes for defining wireless links or channels for a cellular communication system, including TDMA (time-division multiple access), FDMA (frequency-division multiple access), and CDMA (code-division multiple access) schemes. In CDMA communications, different wireless channels are distinguished by different codes or sequences that are used to encode different information streams, which may then be modulated at one or more different carrier frequencies for simultaneous transmission. A receiver can recover a particular stream from a received signal using the appropriate code or sequence to decode the received signal.
Due to the delay-intolerant nature of voice communication, wireless units in conventional cellular systems transmit and receive over dedicated links between a wireless unit and a base station. Generally, each active wireless unit requires the assignment of a dedicated link on the forward link and a dedicated link on the reverse link. Current wireless communications systems are evolving which provide access to packet data networks, such as the Internet, and support a variety of data services. For example, support for multimedia applications (voice, video and data) is important for any network connected to the Internet. These applications have specific requirements in terms of delay and bandwidth. Traditional data applications are typically bursty and, unlike voice communications, relatively delay tolerant. As such, using dedicated links to transmit data is an inefficient use of network resources. Consequently, resource allocation systems have been devised to make more efficient use of network resources using different quality of service (QoS) classes for the different types of traffic based on the delay-tolerant nature of the traffic.
The Universal Mobile Telecommunications System (UMTS) was designed to offer more wireless link bandwidth and QoS features. FIG. 1 shows a typical UMTS network 10 which can be divided into a radio access network (RAN) 12 and a core network (CN) 14. The RAN 12 comprises the equipment used to support wireless interfaces 16a-b between a wireless unit 18a-b and the UMTS network 10. The RAN 12 includes Nodebs or base stations 20a-c, and radio network or base station controllers (RNC) 22a-b. The core network 14 comprises the network elements that support circuit based communications as well as packet-based communications. In establishing a circuit channel to handle circuit-based communications between the wireless unit 18b and a public switched telephone network (PSTN) 24 or another wireless unit, the base station 20b receives (in the uplink) and transmits (in the downlink), the coded information (circuit voice or circuit switched data) over the wireless interface or link 16b. The RNC 22b is responsible for frame selection, encryption and handling of access network mobility. The RNC 22b forwards the circuit voice and circuit switched data over a network, such as an asynchronous transfer mode (ATM)/Internet Protocol (IP) network to a 3G mobile switching center (MSC) 30. The 3G-MSC 30 is responsible for call processing and macromobility on the MSC level. The 3G-MSC 30 establishes the connectivity between the wireless unit 18b and the PSTN 24.
In establishing a packet channel to handle packet-based communications between the wireless unit 18a and a packet data network (PDN) 34, such as the Internet, the base station 20a receives (in the uplink) and transmits (in the downlink), the coded information over the wireless interface or link 16a. In the uplink direction, the RNC 22a reassembles the packets as sent by the wireless unit 18 and forwards them to SGSN 40. In the downlink direction, the RNC 22a receives the packets and segments them into the right size packet to be transferred across the wireless link 16a. The SGSN 40 provides packet data session processing and macromobility support in the UMTS network 10. The SGSN 40 establishes connectivity between the wireless unit 18a and the PDN 34. A GGSN 42 is the gateway to external PDNs. The GGSN 42 acts upon requests from the SGSN 40 for packet data protocol (PDP) session establishment.
As shown in FIG. 2 for the existing network architecture, wireless unit 50 may establish a wireless link with Nodeb1 or base station 52, which is configured to communicate with RNC 54 (RNC1). As such, RNC 54 becomes the serving RNC (SNRC). The wireless unit 50 moves into soft handoff with Nodeb2 or base station 56. Soft handoff refers to the wireless unit simultaneously communicating with more than one base station. As a result, a leg or connection is added between the base station 56 (Nodeb2) and the RNC 54 (RNC1) since the base station 56 is also configured to communicate with the RNC 54 (RNC1). As the wireless unit 50 moves closer to Nodeb3 or base station 58, the wireless unit 50 moves into soft handoff with the base station 58 (Nodeb3), and a leg or connection is added between the base station 58 (Nodeb3) and the RNC 60. Since the base station 58 (Nodeb3) is configured to communicate with RNC 60 only, the uplink traffic will have to move from the base station 58 (Nodeb3) to RNC 54 (RNC1) via RNC 60 (RNC2). The RNC 60 (RNC2) is referred to as the drift RNC (DRNC). The interface between the a base station and an RNC is referred to as the Iub interface, and the interface between two RNCs is referred to as the Iur interface although UMTS Release 99 does not require Iur to support routing. Currently, both the Iub and Iur interfaces are based on ATM, and ATM switches are allowed between Nodebs and RNCs in UMTS Release 99 architecture.
Several drawbacks exist with the current network architecture. First, the SRNC/DRNC concept can result in large differential delays between the legs or connections with the base stations. For example, the delay from the base station 58 (Nodeb3) to the SRNC or RNC 54 is large because of the extra hop between the SRNC 54 and the DRNC 60. To obtain the benefits of soft handoff, packets from the SRNC must reach the three base stations 52 (Nodeb1), 56 (Nodeb2) and 58 (Nodeb3) within a certain time window so that the base stations 52, 56 and 58 can send the packets to the wireless unit 50, and the wireless unit 50 can combine the signals from the three legs. The extra delay could cause the signals over the leg of the base station 58 (Nodeb3) to not provide any soft handoff benefit. Second, when the wireless unit 50 moves sufficiently far from the base stations 52 (Nodeb1) and 56 (Nodeb2) such that the wireless unit 50 no longer communicates with them, a complicated SRNC relocation procedure is used to make the DRNC the new SRNC. Third, if the RNC 54 (RNC1) is congested while the RNC 60 (RNC2) is not, new calls arriving on the base station 52 (Nodeb1) or 56 (Nodeb2) have to be rejected since the base stations 52 or 56 cannot communicate directly to the RNC 60 (RNC2). Finally, when an RNC is down all base stations or Nodebs configured to communicate with the RNC will not be functional.